High dielectric constant glass



Sept. 29, 1959 G. E. RlNDONE-- HIGH DIELECTRIC I CONSTANT GLASS Filed June 28, 1956 IRON LAYEQ GLASS LAYEP 2 OF FUSED n0 5/0 z/vo, K2 0/02 M 0, 02 1/ 0 5/7 0, 5 0

IN V EN TOR: GUY E. R/NDONE BY g ATTORNEY United States Patent 0 HIGH DIELECTRIC CONSTANT GLASS Guy E. Rindone, State College, Pa., assignor, by mesne assignments, to Sylvania Electric Products Inc, Wilmington, Del., a corporation of Delaware Application June 28, 1956, Serial No. 594,581 2 Claims. (Cl. 106-48) This invention relates to glasses suitable as dielectrics, and particularly to glasses of high dielectric constant. The invention especially relates to glasses which can be applied as vitreous enamels in thin coatings upon suitable base materials. 7

Such enamels are especially useful in electroluminescent devices, for example, when used in such devices as a dielectric layer in series with a phosphor-dielectric layer. However, the use of the enamels is not confined to such devices, but has broader application.

The dielectric constant of ordinary glass, of the soda, lime, or silica type is generally about 5. I have discovered, however, that glass of dielectric constant of 15 or more can be obtained with glass from a melt of titanium, silica and boric oxide as the main ingredients, with the addition of zinc, barium or alkaline oxides.

I have further discovered that while such compositions, when applied to a glass base, for example to a glass base having a conductive coating such as the usual stannous chloride or the like, have a dielectric constant of 15, the dielectric constant can be as high as 25,000 or more when the coating is applied to a base of iron, such as a sheet of enamelling steel. This is a tremendous and unexpected increase, which may be due to a partial reduction of the titanium from a valence of four to a valence of three. However, the decrease of valence in other ways, for example, by the addition of metallic iron powder to the glass melt, is much less efiective, although it raises the dielectric constant above the value that the glass would have without it.

The increased dielectric constant obtained with my enamel when coated on an iron base can abso be obtained when the enamel is applied to a metal such as so-called No. 4 alloy, often used for hermetic metal to glass seals, which is only about half iron, the remainder being chiefly nickel and chromium. The composition of No. 4 alloy is given in a printed publication entitled Data Memorandum No. 15, from Superior Tube Co., Norristown, Pennsylvania, dated May 15, 1954, as containing 41.50 to 42.50% nickel, 5.40 to 5.90%.chromium, 0.15 to 0.25% manganese, 0.15 to 0.30% silicon, with maximum permissible amounts of 0.07% carbon, 0.025% phosphorous, 0.025% sulfur, 0.15% aluminum, and the balance iron.

The high dielectric constant of my new glass or enamel appears to be due to some of the materials being present in the glass in the crystal phase. When zinc or barium oxides are used in the glass melt, some zinc titanate (Zn0.Ti0 or barium titanate (BaO.2TiO appears to be formed, with rutile or anatase in lesser amounts.

' The presence of large amounts of rutile or anatase, however, appears detrimental to the formation of material of high dielectric constant.

The heat treatment of the glass melt is an important factor in obtaining a high dielectric constant. The ingredients can be fused at a temperature between about 1050 C. to 1450 C. for one to 3 hours, and then cooled quickly for example, by being quenched in water.

Patented Sept. 29, 1959 Grams TiO 694 SiO 788 H BO 855 ZnO 1043 a)2 5 98 K CO 167 Other compounds than those specified can be used, in general either oxides or compounds reducible to the oxides, such as carbonates.

The ingredients are mixed intimately by being rolled dry in a drum for about one hour. The mixture is then melted at a temperature of about 1290 C. for about 2 hours, although the temperature can be between about -1050 C. and about 1450 C. and the time can be between about one and three hours, the longer time being generally used with the lower temperature, and vice versa.

The melt is then quenched by being poured into water at room temperature. The shock of quenching will break up the melt into generally small particles, say about li inch in particle size.

The resultant glass frit is then dried, and about 1500 grams of it is mixed with enough amyl acetate to make a suspension of about 1000 cc. and milled in a one-quart ball-mill for between about two to three days, about 60 hours generally being enough for proper mixing. The material is then passed through a screen to limit the particle size, the screen being, for example of ZOO-mesh.

The suspension, with addition of a further but small amount, generally about 500 cc., of amyl acetate, to bring the suspension to a spraying consistency, is sprayed onto the base material, which can be, for example, a sheet of enamelling steel, which may conveniently be of the standard 0.012 inch or 0.030 inch thickness, although the thickness is not critical.

It the resultant piece is to be part of an electroluminescent device, the coating should be sprayed to a thickness of about 4 to 6 one-thousandths of an inch. This will generally require the spraying of about 0.2 gram per square inch of base area. The coating is then dried and fired at between 750 C. to 800 C. for one to three minutes, the longer time being preferably used with the lower temperature, and vice versa. Firing of 800 C. for about one minute will be satisfactory. The enamel coating 2 will be fused to the metal base 1 by the firing.

The coating will have a blueish tint, due to reduction of the titanium, and if sprayed onto enamelling steel will have a diaelectric constant of many thousands.

Where the enamel is to be used on other than an iron base, a small amount, say /z% by weight of fine iron: particles, which can be fine enough to pass through a 200- mesh screen, can be added to the original batch.

The ingredients in the initial mix may be varied overthe following ranges with good results.

. Mol percent Ti0 Although the'alkaline' oxide listed above is of potas sium; sodium or lithium can also either separately, or with the posassium, or with each other, or all three can be used, the total alkaline oxide beingbetween about 2 to about 14' withgood' results:

Withsom'eof the above mixtures the firing temperature of the sprayed coating maybe as low as 550' C., if the fi'ri'ng" time is about ten minutes.

The leakage resistance of the dielectriclayer produced by my invention will generally be between several hundred ohms and several thousand ohms, for a thickness of layer of about 4 to 6 one thousandths of an inch; and an area of 12 square inches.

What I claim is:

11 A glass of high dielectric constant, said glass comprisingabout 1-9 to- 36 mol percent TiO about 20- to 37- mol percent SiO- about 1 to Z9 mol percent ZnO, about 2- to 14- mol percent potassiumoxide, about (Ho 10 molpercent barium oxide, andabout 4- to 21' mol percent bor-ic oxide;

References Cited in the file of this patent UNITED STATES PATENTS 1,524,134 Hutchins Ian. 27, 1925 1,955,821 McDougal' Apr. 24, 1934 2,262,069 Turk NOV. 11, 1941 FOREIGN PATENTS 446,970 Great Britain May 6, 1936 

1. A GLASS OF HIGH DIELECTRIC CONSTANT, SAID GLASS COMPRISING ABOUT 19 TO 36 MOL PERCENT TIO2 ABOUT 20 TO 37 MOL PERCENT SIO2, ABOUT 1 TO 29 MOL PERCENT ZN/, ABOUT 2 TO 14 MOL PERCENT BARIUM OXIDE, AND ABOUT 4 TO 21 MOL 10 MOL PERCENT BARIUM OXIDE, AND ABOUT 4 TO 21 MOL PERCENT BORIC OXIDE. 